Low volume on 645 console w/P-P 42's - Printable Version

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+--- Thread: Low volume on 645 console w/P-P 42's (/showthread.php?tid=844)

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Low volume on 645 console w/P-P 42's - Guest - 11-20-2007

I have finally gotten all caps and resistors replaced in this chassis and fired it up last night. Had no reception and right away noticed that two tubes were not lit: one of the 42's and the 85. I pulled and tested all the tubes in my tube tester. The 85, it turned out, just was not seated fully in its socket. The 42 that did not light had an open filament, while the other 42 lit in the tube tester but would not move the tester needle. I found one 42 in my box to replace the open one so now I have one strong output tube and one, for all practical purposes, which is dead. But I got some reception on all three bands using the longwire I installed in my basement shop. But, with the volume control fully on the volume is just listenable, not nearly the level it should be. Would the imbalance between the 42 outputs result in this kind of volume problem? Or (as I'm more likely to suspect) is there probably an open coil winding somewhere? I checked continuity on all coil windings and the input/output transformers, but I could have missed something...
Thanks for any help that can be offered!

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- Ron Ramirez - 11-21-2007

Hi Vinton, and welcome!

You did check continuity of audio interstage transformer (52), correct?

Check the plate voltage of the Type 85 (should be 82 volts), and plate and screen voltages of the two Type 42 outputs. It wouldn't hurt to check the output transformer (55) for continuity also, if you have not yet done so.

Does your radio have the correct speaker? The speaker field is only 435 ohms in this model.

The audio level should be quite listenable (i.e. decent volume) even with only one Type 42 operating. But do remove the inoperative Type 42 before proceeding further.

I doubt it is a coil problem, since each band uses separate windings instead of multi-tapped coils.

Also check the AVC circuit; make sure resistors and capacitors in the AVC line were reconnected properly.

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